1. Field of the Invention
The present invention relates to a method for manufacturing metal cylinder members of electron tubes and a method for manufacturing magnetron anodes.
2. Description of the Related Art
In general, various electron tubes and their vacuum envelopes, various electrodes, such as anodes and grids, resonant cavities, high-frequency waveguides, etc. are partially provided with metal cylinder members.
As is generally known, the anode structure of a magnetron for a microwave oven, for example, is formed of an anode cylinder, a plurality of anode vanes radially arranged on the inner face of the cylinder, and a plurality of resonant cavities corresponding to the number of vanes.
Available as the material for the anode structure are copper, aluminum, etc. which have high electric and thermal conductivity characteristics. In general, copper is preferred because of its higher heat resistance.
In one conventional method for manufacturing the magnetron anode structure, an anode cylinder of a given length is cut from an elongated cylinder or pipe, the inner and outer faces and both open end portions of the anode cylinder are shaved into predetermined configurations, and anode vanes are brazed to the inner peripheral surface of the cylinder.
According to this method, however, manufacture of the cylinder material requires much labor, and if the dimensional accuracy of the cylinder material is not high enough, the completed cylinder must be finished again to the necessary inside and outside diameters for an anode cylinder, thus inevitably entailing an increase in the cost of the product.
Accordingly, a novel method for manufacturing the magnetron anode has already started to be put into practice, in which an anode cylinder is formed by rolling up a plate or material and sealing the opposite end portions thereof. According to this method, manufacture of the plate material is easy, the cylinder can be formed to a desired diameter, and the plate thickness can be controlled during the rolling process. Thus, the cost of the product can be effectively reduced.
FIGS. 1(a) to 1(k) show processes of the conventional manufacturing method, as disclosed in U.S. Pat. No. 4,570,843 issued on Feb. 18, 1986. As shown in FIG. 1(a), an elongated sheet is first cut to a predetermined length l to obtain a copper plate. Thickness t1 of plate 1 is just a little greater than the wall thickness of the anode cylinder as a product, and its length l is equal to or just a little greater than the circumferential length of its medial line. Plate 1 is a hexahedron whose adjacent faces extend basically at right angles to one another.
The anode cylinder is formed from plate 1 in the following processes, and finally, anode vanes are brazed to the cylinder.
The individual processes will be described in succession. As shown in FIG. 1(b), plate 1 is rolled into cylinder 2. In this stage, the opposite end faces of plate 1 are not fully in intimate contact with the cylinder, leaving a V-shaped gap S1 between them.
After undergoing a drawing or reduction forming process, cylinder 2 is cooled to room temperature to obtain cylinder 3, as shown in FIG. 1(c). In this process, gap S3 of seam 6 is adjusted to a very small size.
Thereafter, in the compression forming process shown in FIG. 1(d), cylinder 4 is subjected to an axial compressive force to correct its wall thickness and out of roundness. Thus, cylinder 5 shown in FIG. 1(e) is obtained. In FIG. 1(d), numerals 7, 8 and 9 denote a punch, a fixed die, and a die-and-knockout, respectively.
Subsequently, cylinder 5 is advanced to a process for shaving the open end portions and the inner and outer peripheral surfaces of cylinder 5 to predetermined shapes and dimensions, as shown in FIG. 1(f).
Then, diametrical external force W2 is outwardly applied to cylinder 5 to create gap S4 at seam 10, as shown in FIG. 1(g), and the whole surface of cylinder 11, including the inside seam 10, is degreased and washed or cleaned, as shown in FIG. 1(h).
Then, brazing material 12 is inserted into seam 10, as shown in FIG. 1(i).
After brazing material 12 is inserted in this manner, it can be held in position by the spring-back force of cylinder 11 when external force W2 is removed. This state is shown in FIG. 1(j).
Finally, a brazing process is performed, as shown in FIG. 1(k).
This manufacturing method, however, requires a large amount of silver or gold solder, which is relatively expensive. If a narrow gap remains at seam 10, moreover, the brazing is imperfect, so that airtightness cannot be maintained.
Accordingly, methods for welding the seam by means of a high-energy beam such as an electron beam instead of brazing the seam are disclosed in, for example, Japanese Patent Disclosure No. 156635/81 and Japanese Patent Publication No. 34779/85.
According to these manufacturing methods, however, weld beads remain locally projecting from the inner and outer peripheral surfaces of a magnetron anode, so that the wall thickness is not uniform enough for satisfactory out of roundness. Thus, the beads must be removed by shaving in the final stage.